High Pressure, Single Stage Rotor

ABSTRACT

Rotors for a rotary screw compressor having geometries that increase the efficiency of the compression process. The thermodynamic behavior of the rotors may be improved through an increase in the number of male and female lobes of the rotors and/or by an increased wrap angle, such as, for example, using wrap angles that exceed 360 degrees. By increasing the number of lobes, the rotors may have improved resistance to bending of the rotors that may otherwise occur when the temperature of the rotors is elevated and/or the rotor is utilized in relatively high pressure compression applications. The improved resistance to bending may allow the rotors to retain the relatively small size of the work spaces between intermeshed lobes of the rotors in which captured working fluid is being compressed.

BACKGROUND

Embodiments of the present invention generally relate to the configuration of screw compressor rotors that are configured to compress a working fluid to a high discharge pressure. More specifically, embodiments of the present invention relate to adjustments to the geometry of the helical screw portion of direct cooled screw compressor rotors to improve the efficiency of the compression process.

Conventional rotary screw compressors often use intermeshing rotors to compress a working fluid. More specifically, a working fluid entering into a compression chamber of the compressor may be captured in a work space between the rotors and housings. The captured working fluid may then be displaced along the rotors as the rotors are rotated. Further, the rotors are typically configured to reduce the volume of the work space in which the captured working fluid is contained as the working fluid is displaced along the rotors, thereby compressing the working fluid.

As described by physical gas laws, the temperature of a working fluid will typically increase as the working fluid is compressed. Such increases in the temperature of the working fluid may also elevate the temperature of the rotors. Yet, as the temperature of the rotors increase, the ability of the rotors to relatively efficiently compress the working fluid may decrease, particularly in relatively high pressure applications. Moreover, in high pressure applications, such as, for example, applications in which the rotors compress working fluid up to about eleven bar absolute, elevated rotor temperatures may cause a reduction in the stiffness in the rotor. In such situations, the rotors may have an increased propensity to bend or deflect, which may thereby increase the size of the work space between the intermeshing rotors in which the captured working fluid is being compressed. Such increases in the size of the work space may decrease the efficiency of the compression process, as well as increase the potential for backflow of the captured working fluid.

BRIEF SUMMARY

An aspect of the present invention is a rotary screw compressor system that includes a male screw rotor that has a male helical screw portion. The male helical screw portion may include a plurality of male lobes and a male rotor wrap angle. According to certain embodiments, the plurality of male lobes may be between four and eight lobes, inclusive, and the male rotor wrap angle is between approximately 350 degrees and 450 degrees, inclusive. The rotary screw compressor system may also include a female screw rotor that has female helical screw portion that is configured to intermesh with the male helical screw portion. Further, the female helical screw portion may include a plurality of female lobes and a female rotor wrap angle.

Another aspect of the present invention is a single stage, direct cooled rotary screw compressor system that includes a male screw rotor that has a male helical screw portion. The male helical screw portion may include at least four male lobes and a male rotor wrap angle that is between approximately 350 degrees and 450 degrees, inclusive. Further, the single stage, direct cooled rotary screw compressor system may also include a female screw rotor having a female helical screw portion that is configured to intermesh with the male helical screw portion. The female helical screw portion may include a plurality of female lobes and a female wrap angle between approximately 250 degrees and approximately 325 degrees, inclusive.

Another aspect of the present invention is a rotary screw compressor system for compressing a working fluid. The rotary screw compressor system may include a compressor, as well as a male screw rotor that has a male helical screw portion. The male helical screw portion includes a plurality of male lobes and a male rotor wrap angle. Additionally, the rotary screw compressor system includes a female screw rotor that has a female helical screw portion that is configured to intermesh with the male helical screw portion within the compression chamber to compress the working fluid to a discharge pressure. The female helical screw portion includes a female rotor wrap angle and a plurality of female lobes. Further, at least one of the male rotor wrap angle and the female rotor wrap angle is between approximately 250 degrees and 450 degrees, inclusive. The rotary screw compressor system also includes a coolant system that is configured to circulate a coolant to the compression chamber to cool a temperature of at least a portion of the working fluid that is being compressed in the compression chamber.

Other aspects of the present invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic of a single stage, direct cooled rotary screw compressor system that is configured to compress a working fluid according to embodiments of the present invention.

FIG. 2 illustrates a cross sectional view of a male screw rotor engaged with a female screw rotor according to embodiments of the present invention.

FIG. 3 illustrates a perpendicular to axis cross sectional view of an engagement of male and female screw rotors according to embodiments of the present invention.

FIG. 4 provides a chart illustrating the discharge pressure of a compressed working fluid as a function of the number of lobes of the male and female screw rotors.

FIG. 5 provides a chart illustrating the discharge pressure of a compressed working fluid as a function of the wrap angle of a male screw compressor rotor.

The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentalities shown in the attached drawings.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates a schematic of a single stage, direct cooled rotary screw compressor system 10 that is configured to compress a working fluid, such as, for example, ambient air. According to certain embodiments, the rotary screw compressor system 10 may include a compressor housing 12, a separator 14, a drive system 16, a gear system 18, a coolant system 20, and a lubrication system 22. The compressor housing 12 may include a compression chamber 24 that has a suction side 26 and a discharge side 28. Further, the compressor housing 12 may house at least a portion of a plurality of screw compressor rotors 30. In the illustrated embodiment, the plurality of screw compressor rotors 30 include at least one male rotor 32 and at least one female rotor 34.

Referencing FIG. 2, the male screw rotor 32 may include first and second shafts 38 a, 38 b that extend from opposing sides of a helical screw portion 40 of the male screw rotor 32. Similarly, the female screw rotor 34 may also include first and second shafts 42 a, 42 b that extend from opposing sides of a helical screw portion 44 of the female screw rotor 34. At least the helical screw portions 40, 44 of the male and female screw rotors 32, 34 are housed within the compression chamber 24.

A power source 46 of the drive system 16 may provide power for the rotational displacement of the screw compressor rotors 32, 34. A variety of different power sources 46 may be employed, including, for example, an electric motor, an internal combustion engine, or a turbine, among other power sources. According to certain embodiments, rotational power from the power source 46 may be transmitted directly or indirectly from the power source 46 to the male screw rotor 32. Additionally, the male screw rotor 32, such as, for example, a shaft 38 b of the male screw rotor 32, may be operably coupled to a gear system 18, which may be used to rotatably displace the female screw rotor 34. Moreover, according to certain embodiments, the transmitted power from the power source 46 may be provided via rotation of the male screw rotor 32 to rotate timing gears of the gear system 18 that are configured to at least assist in transmitting power to the female screw rotor 34 in a manner that maintains the rotational displacement of the screw compressor rotors 32, 34 in proper alignment. Additionally, the gear system 18, as well as bearings that may be disposed on or about the shafts 38 a, 38 b, 42 a, 42 b, may be lubricated by a lubricant that is provided and/or circulated by the lubrication system 22.

The screw compressor rotors 32, 34 are configured to capture working fluid between the helical screw portions 40, 44 of the screw compressor rotors 32, 34. As the screw compressor rotors 32, 34 rotate, the captured working fluid travels along the rotating helical screw portion(s) 40, 44 and toward the discharge side 28 of the compressor housing 12. As discussed below, as captured working fluid travels along the rotating helical screw portion(s) 40, 44, the size or volume of the work space between the intermeshing rotors 40, 44 that is occupied by the captured working fluid is reduced, thereby causing the captured working fluid to be compressed. Further, as the working fluid is compressed, the temperature of the working fluid, and thus the temperatures of the male and female screw rotors 32, 34, increases. In an attempt to remove at least some heat generated by the compression of the working fluid, according to certain embodiments, a coolant, such as, for example water or a water based coolant, from the coolant system 20 may be circulated into and/or about the compression chamber 24 to directly cool the working fluid or otherwise circulate the coolant about the compression chamber 24, such as, for example, in a sleeve.

After being compressed within the compression chamber 24 to a discharge pressure, the compressed working fluid may pass through an outlet 48 on a discharge side 28 of the compression chamber 24 before being processed within the separator 14. The separator 14 may be configured to withdraw coolant, contaminates, or other items or materials from the compressed working fluid. The compressed working fluid may then be discharged from the rotary screw compressor system 10 via an outlet line 50 so that the compressed working fluid may be delivered to machinery and/or equipment that may utilize and/or store the compressed working fluid.

Although a particular configuration of the rotary screw compressor system 10 has been illustrated and described herein, it should be understood that other configurations are also contemplated. For example, according to certain embodiments, the rotary screw compressor system 10 does not include a coolant system 20 that is configured to remove heat from the working fluid. Further, according to certain embodiments, the rotary screw compressor system 10 does not include a lubrication system that 22 delivers lubricant to the compressor housing 12. Further, according to certain embodiments, the rotary screw compressor system 10 may include a plurality of male screw rotors 32 and/or a plurality of female screw rotors 34.

Referencing FIGS. 2 and 3, the helical screw portion 40 of the male screw rotor 32 may include a plurality of helically extending male lobes 52. Further, as shown in FIG. 3, the male lobes 52 may each have a generally bulbous shape, among other shapes. Similarly, the female screw rotor 34 may include a plurality of helically extending female lobes 53 that provide recesses 54 therebetween, the female lobes 53 and/or the recesses 54 being configured so that the curvatures of the bulbous shape of the male lobes 52 may be received within the recesses 54 as the male and female screw rotors 32, 34 are each rotated about their respective longitudinal central axis 35 a, 35 b. Further, the number of female lobes 53, and associated recesses 54, on the female screw rotor 34 may be greater than the number of male lobes 52 on the male screw rotor 32. For example, according to certain embodiment, the male screw rotor 32 may have five male lobes 52, while the female screw rotor 34 includes seven female lobes 53. Thus, according to certain embodiments, the gear system 18 may be configured so that the female screw rotor 34 rotates at a faster speed than the male screw rotor 32.

According to certain embodiments, the male lobes 52 may generally not physically contact the female lobes 53 or the recesses 54 of the female screw rotor 34. Further, the size of the clearance, or work space, between the male lobes 52 and the female lobes 53 is reduced along the helical screw portions 40, 44 of the male and female screw rotors 32, 34. More specifically, the work space between the bulbous shaped male lobes 52 and the female lobes 53 toward the suction side 26 of the compression chamber 24 may be larger than the work space between the male lobes 52 and the female lobes 53 at discharge side 28 of the compression chamber 24. Such changes in the size of the work space may be provided by a relatively gradual increase in the size of the male lobes 52 and/or a decrease in the size of the recesses 54 along the helical screw portions 40, 44 of the male and female screw rotors 32, 34, respectively. Moreover, such changes in the size of the male and female lobes 52, 53 may reduce the volume of the work space, and thus reduce the volume of the working fluid, thereby compressing the working fluid.

Embodiments of the present invention provide screw compressor rotors 32, 34 in which the geometry of the helical screw portions 40, 44 have been changed through an increase in the number of male and female lobes 52, 53 of the male and female screw rotors 32, 34. For example, FIG. 4 illustrates the relationship of the pressure of compressed working fluid that is discharged from a compressor housing 12 as a function of the number of male and female lobes 52, 53. As shown, intermeshing mating screw compressor rotors 32, 34 that utilize four male lobes 52 on the male screw rotor 32 and six female lobes 53 on the female screw rotor 34 have a higher discharge pressure for the compressed working fluid than similar mating screw compressor rotors 32, 34 that have three male lobes 52 and four female lobes 53. As shown by FIG. 4, the discharge pressure of the working fluid is further increased when the four male lobes 52 and six female lobes 53 are replaced with five male lobes 52 and seven female lobes 53.

Such demonstrated elevation in discharge pressures may at least in part be attributed to an increase in the stiffness of the male and female screw rotors 32, 34 that is attained by increasing the number of male and female lobes 52, 53. For example, an increase in the number of male and female lobes 52, 53 may translate into a larger root diameter (R_(d)) on the helical screw portions 40, 44 of the male and female screw rotors 32, 34, thereby enhancing the stiffness of screw rotors 32, 34. Further, increasing the number of male and female lobes 52, 53 may also lead to an increase in the amount of material used to provide the male and female lobes 52, 53. Such material increases may decrease the overall size of the empty space of the recesses 54, as well as the size of similar gaps 51 between the male lobes 52, and thereby further enhance the stiffness of the associated male and female screw rotors 32, 34. Moreover, by reducing the size of the gaps 51 and recesses 54, each male and female lobe 52, 53 may be in relatively closer proximity to adjacent lobes 52, 53 on the same screw rotor 32, 34, thereby allowing the adjacent lobes 52, 53 to provide enhanced support in resisting deflection of the male and female screw rotors 32, 34.

The efficiency of the rotary screw compressor system 10 may, at least in part, be effected by the size of the work space between intermeshed male and female lobes 52, 53 of the screw rotors 32, 34 that contains the working fluid that is being compressed. Moreover, an increase in the size of the work space, such as, for example, an increase in the size of the work space due to the bending of one or both of the rotors 32, 34, may decrease the efficiency of the compression process, as the resulting larger work space typically equates to a larger area for the working fluid to occupy. Thus, the ability to improve the stiffness of the male and female screw rotors 32, 34 may allow for the male lobes 52 and the female lobes 53, or associated recesses 54, to maintain smaller inter-lobe clearances, or gap heights, between the lobes 52, 53, and thereby maintain smaller work spaces.

FIG. 5 provides a chart illustrating the discharge pressure of a compressed working fluid as a function of the wrap angle of the male screw compressor rotor 32. More specifically, FIG. 5 demonstrates an increase in the wrap angle of the male screw rotor 32 translating into an increase in the discharge pressure of the working fluid. For example, as shown, an increase in the wrap angle of a male screw rotor 32 from 350 degrees to 400 degrees may translate into an increase in the discharge pressure of working fluid that is compressed by intermeshed male and female screw rotors 32, 34. As also shown, a further increase in the wrap angle of the male screw rotor 32 from 400 degrees to 450 degrees also translates into a further elevation of the discharge pressure of the compressed working fluid. More specifically, the use of relatively high wrap angles, such as, for example wrap angles that exceed approximately 360 degrees, may allow for a reduction in internal gas losses, particularly when compared to more common wrap angles of approximately 270 degrees to 300 degrees for compressors that operate without the supply of a coolant. For example, such increases in the wrap angle, in addition to increases in the number of lobes 52, 53, may at least assist in preventing captured working fluid from flowing back toward lower pressure work spaces along the intermeshed lobes 52, 53 of the male and female screw rotors 32, 34.

Such reduction in internal gas losses may both reduce the power consumption of the compressor while also increasing the efficiency of the compression process. For example, as previously discussed, the reduction in back flow that may be attained by using an increased number of male and female lobes 52, 53 and by using wrap angles in excess of 360 degrees may minimize back flow. By reducing the potential for back flow, the captured working fluid has less of an opportunity to flow back to lower pressure work spaces, and thereby is prevented from expanding, which would otherwise require additional compressor power for re-compressing the expanded working fluid.

While the foregoing was discussed in terms of the wrap angle of the male screw rotor 32, similar increases in discharge pressure of the compressed working fluid may also be realized through an increase in the wrap angle of the female screw rotor 34. For example, according to certain embodiments, a male screw rotor 32 may have five male lobes 52 and a wrap angle of about 350 degrees to about 450 degrees, while the female screw rotor 34 may have seven female lobes 53 and a wrap angle of about 250 degrees to about 325 degrees.

Thus, as shown by at least FIGS. 4 and 5, changing the geometry of the profile of the male and female screw rotors 32, 34, such as, for example, by increasing both the number of male and female lobes 52, 53 and the wrap angle of the male screw rotor 32 and/or female screw rotor 34 may increase the efficiency of the compression process. Moreover, such changes may minimize bending and/or deflection of the male and female screw rotors 32, 34 during compression of working fluid, and in particular during high pressure compression applications, such as, for example, applications in which the compressed working fluid has a discharge compression of approximately 11 bars absolute.

Various features and advantages of the present invention are set forth in the following claims. Additionally, changes and modifications to the described embodiments described herein will be apparent to those skilled in the art, and such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its intended advantages. While the present invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered illustrative and not restrictive in character, it being understood that only selected embodiments have been shown and described and that all changes, equivalents, and modifications that come within the scope of the inventions described herein or defined by the following claims are desired to be protected.

While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A rotary screw compressor system comprising: a male screw rotor having a male helical screw portion, the male helical screw portion having a plurality of male lobes, the plurality of male lobes being between four to eight males lobes, inclusive, and a male rotor wrap angle between approximately 350 degrees to 450 degrees, inclusive; and a female screw rotor having a female helical screw portion configured to intermesh with the male helical screw portion, the female helical screw portion having a plurality of female lobes and a female rotor wrap angle.
 2. The rotary screw compressor system of claim 1, wherein the female rotor wrap angle is between approximately 250 degrees and approximately 325 degrees, inclusive.
 3. The rotary screw compressor system of claim 1, wherein the number of female lobes of the plurality of female lobes is greater than the total number of male lobes of the plurality of male lobes by one or two female lobes.
 4. The rotary screw compressor system of claim 1, wherein the plurality of male lobes comprises at least five male lobes.
 5. The rotary screw compressor system of claim 1, wherein the plurality of female lobes comprises between five to ten female lobes, inclusive.
 6. The rotary screw compressor system of claim 5, wherein the male helical screw rotor and female helical screw rotor are configured to intermesh to compress a working fluid to approximately 11 bar absolute.
 7. The single stage, direct cooled rotary screw compressor system of claim 1, wherein the male helical screw rotor and female helical screw rotor are configured to intermesh to compress a working fluid to approximately 11 bar absolute.
 8. A single stage, direct cooled rotary screw compressor system comprising: a male screw rotor having a male helical screw portion, the male helical screw portion having at least four male lobes and a male rotor wrap angle, the male rotor wrap angle being between approximately 350 degrees and 450 degrees, inclusive; and a female screw rotor having a female helical screw portion configured to intermesh with the male helical screw portion, the female helical screw portion having a plurality of female lobes and a female wrap angle between approximately 250 degrees and approximately 325 degrees, inclusive.
 9. The single stage, direct cooled rotary screw compressor system of claim 8, wherein the number of female lobes of the plurality of female lobes is greater than the total number of male lobes of the plurality of male lobes by one or two female lobes.
 10. The single stage, direct cooled rotary screw compressor system of claim 9, wherein the female rotor wrap angle is at least 360 degrees.
 11. The single stage, direct cooled rotary screw compressor system of claim 8, wherein the male helical screw rotor and female helical screw rotor are configured to intermesh to compress a working fluid to approximately 11 bar absolute.
 12. The single stage, directed cooled rotary screw compressor system of claim 11, wherein the male rotor wrap angle is between approximately 420 degrees and 450 degrees, inclusive.
 13. A rotary screw compressor system for compressing a working fluid, the rotary screw compressor system comprising: a compression chamber; a male screw rotor having a male helical screw portion, the male helical screw portion having a plurality of male lobes and a male rotor wrap angle; a female screw rotor having a female helical screw portion configured to intermesh with the male helical screw portion within the compression chamber to compress the working fluid to a discharge pressure, the female helical screw portion having a female rotor wrap angle and a plurality of female lobes, at least one of the male rotor wrap angle and the female rotor wrap angle being between approximately 250 degrees and 325 degrees; and a coolant system configured to circulate a coolant to the compression chamber to cool a temperature of at least a portion of the working fluid that is being compressed in the compression chamber.
 14. The rotary screw compressor system of claim 13, wherein only the male rotor wrap angle is between approximately 350 degrees and 450 degrees.
 15. The rotary screw compressor system of claim 13, wherein the male rotor wrap angle is between approximately 420 degrees and 450 degrees.
 16. The rotary screw compressor system of claim 13, wherein the number of female lobes of the plurality of female lobes is greater than the total number of male lobes of the plurality of male lobes by one or two female lobes.
 17. The rotary screw compressor system of claim 16, wherein a ratio of the plurality of male lobes to the plurality of female lobes is 5:7.
 18. The rotary screw compressor system of claim 13, wherein the plurality of female lobes is between five and ten female lobes, inclusive and the plurality of male lobes is between four and eight male lobes, inclusive.
 19. The rotary screw compressor system of claim 18, wherein the discharge pressure is approximately 11 bar absolute.
 20. The rotary screw compressor system of claim 13, wherein the discharge pressure is approximately 11 bar absolute. 